1. Field of the Invention
The present invention relates to a core sampler, particularly for use in oil prospecting, comprising, particularly at its front end associated with a coring bit, for grasping a core sample to be brought to the surface:
a deformable moving ring having a cylindrical internal surface designed to clamp the core sample, particularly when the latter is made of a so-called consolidated substance, and a frustoconical external surface which tapers toward the front end, PA1 a cavity which has a wall with an internal cone frustum-shaped bearing surface corresponding in terms of its shape and size to the external frustoconical surface of the moving ring, which is fixed to the core sampler at least in the longitudinal direction thereof and in which the moving ring can be housed in such a way that it can occupy, in the longitudinal direction, two extreme positions, one being a clamping position in which the moving ring pressed, on its small-diameter side, into the internal cone frustum is deformed inward so as to reduce its internal cross section and thereby clamp the core sample in order to immobilize it at this point in the core sampler. PA1 in the other extreme position, known as the starting position, the moving ring is exposed to zero or minimal strain from the bearing surface and has an inside diameter not smaller than the outside diameter of the core sample to be grasped, and PA1 the core sampler comprises control means designed to move the moving ring in the longitudinal direction from the extreme starting position as far as the extreme clamping position. PA1 a deformable sleeve, PA1 means which can be controlled in order to deform the deformable wall inward by applying a force to it, so as at least to clamp the core sample in order to fix thereto.
2. Background of the Prior Art
A significant drawback of a core sampler of this kind, known at this time from patent application FR-A-2 088 255 (FIG. 1B) arises from the fact that the deformable moving ring is usually an elastic ring with a frustoconical external surface, split longitudinally and the inside diameter of which is smaller than the nominal inside diameter of the core sampler or than the outside diameter of a core sample made of consolidated substance, cut by the core sampler. The core sample which is formed has therefore to be pushed into the split ring in such a way as to open up this ring and keep it open. Blockage, known to the person skilled in the art, of the core sample in the split ring, and therefore in the core sampler, can therefore occur as a result of the constant friction between the core sample and the split ring and as a result, for example, of core-sample debris which may move therein because of this and become wedged between the core sample and the end of one of the slits if these slits are not made over the entire length of the ring. An expensive core-sampling operation may be completely compromised by this blockage. What is more, in the case of an unconsolidated core sample (sand, etc.), this smaller inside diameter of the deformable ring slows the progress of the core sample and upsets the original arrangement of its constituents, and this therefore considerably compromises the efficiency and results of the core-sampling.
Another significant drawback of the known core sampler arises from the complexity of producing a flattenable sheath as described in patent application FR-A-2 088 255, even an elastic one, because clearly, for a given circumference that allows a cylindrical core sample (FIG. 1B) to be housed, the sheath may have difficulty in adopting a flattened position where the largest transverse dimension is equal to twice the diameter of the aforementioned circumference. Furthermore, the flexibility imposed on the sheath means that the core sampler fluid system has to be kept under pressure while this sampler is being raised, and even for longer than this, until a complex handling operation, not explained, has been performed, if the core sample is not to be disturbed over a significant part of its length starting at the point where the sheath was flattened.
In addition, the aforementioned document neither shows nor suggests any interaction between the split ring and the flattenable sheath.